The invention relates to a method for generating a control output for a position control loop or circuit and to an apparatus for carrying out such a method.
Nater et al., published European Patent Application No. EP 390,969, discloses a method of this type, according to which a measuring beam, which is produced by a light source, is reflected by a movable test object in the form of a mirror and reaches a position-sensitive light detector. The measuring beam is focused on the light detector by an optical system. The measured values obtained by the light detector are supplied to a computer or signal processor, in which a position signal corresponding to the geometric center or the maximum of the intensity distribution of the focused measuring spot is determined by interpolation. The analog signals of the light detector are supplied directly to the signal processor and are initially processed in analog form, with signals corresponding to the desired position being included in addition, to obtain a digital, interpolated signal corresponding to the determined position of the focal spot. The interpolated signal is supplied to a control loop to control the test object. This document contains no indication that a function which corresponds to the function of the actual intensity distribution of the measuring beam on the light detector should be taken into account. Furthermore, the analog signals are supplied directly to the signal processor.
Brunk, published German Patent Application No. DE 42 12 066A, discloses a method and an apparatus for determining the position of an optical line according to which an image containing the optical line is recorded line-by-line with a video camera to generate a video signal and a pixel clock. A digital representation of the optical line is determined from the video signal. The video camera is oriented in such a way that the lines of the video camera cross the optical line. There is no position control and no determination of a position signal by interpolation, and no suggestion is made of such a combination of features.
The book entitled Bauelemente der Optik, Taschenbuch fü{umlaut over (r)}r Konstrukteure [Components in Optics, Pocket Edition for Designers], H. Naumann and G. Schröder, 4th edition, Hanser-Verlag, 1983, describes a method that is also known as the autocollimation method and permits the measurement of the angular position of rotating mirrors. A beam collimated by a collimation lens is reflected as a measuring beam on the mirror to be measured, and the angle of the reflected beam to the incident light beam as it passes back through the collimation lens is converted into position information. This information conversion, however, introduces an additional error source in the form of lens errors into the measurement. A computational correction of such errors prolongs the computing time required to determine the information corresponding to the momentary angular position of the rotating mirror.
Minoura et al., U.S. Pat. No. 4,318,582, further discloses a two-dimensional scanning apparatus comprising two rotating mirrors for deflecting a light beam of a light source, particularly a laser, in two substantially perpendicular directions. The rotating mirrors are rotated by electrical drives. To determine the angular position of the rotating mirrors, signal generators are provided, which are coupled with the drive shafts of the electric drive motors. The information recorded by the signal generators is supplied to the corresponding position control loop of the respective rotating mirror. Such signal generators for detecting the angular position of a shaft are typically inductive or electromagnetic position sensors, which require highly precise manufacturing and rarely satisfy today's accuracy requirements in practice, or can satisfy them only at high manufacturing costs.